Low-water alarm



H. B. THURSTON LOW WATER ALARM Filed July 18, 1924 -7 22/ MBA/TOT?Patented Julv 13; 1926.

UNITED, STATES 1,592,583 PATENT OFFICE.

HERMAN B. THUBSTON, OF CLEVELAND, OHIO, ASSIGNOR TO THE TA'LMA GE MANU-FACTURING COMBANY, F CLEVELAND, OHIO, A CORPORATION OF OHIO.

LOW-WATER ALARM.

Application flledluly 18, 1924. Serial No. 726,710.

This invention relates to low 1 water alarms for use in connection withsteam boilers and constitutes an improvement over low water alarmdevices, now in use. Particularreference is made to my prior ap-.

pliqcztion, Serial No. 701,598 filed-March 24,

In this and a prior application, also of my own, namely Serial No.643,512, filed June 5, 1923, are shown a conduit leading from the steamchamber of the boiler to a cage located near the crown sheet, and

which contains a fusible element normally closing the conduit. A passageleading from this point communicates with an I alarm device-such asawhistle. Whenever the element becomes fused by the heat of the crownsheet, steam thus released travels along the passage and sounds thealarm. This occurs when the water inthe boiler reaches a dangerously lowlevel.

The present invention relates particularly to an improved means forsupporting the fusible element and for providing communication betwenthe conduit leading from the steam space and the outlet passage, whichimprovements present certain advantages as will hereinafter appear.

vention to provide a fusible plug cage in heat of the boiler fusing theplug prior to the water in the boiler reaching the danger leveland whichwill by virtue of this conboiler when the danger level is reached. 4 Itis another object to provide a more open pgssageway for the" meltedmetal of the sible plug.

7 A further object is to provide an open plug cage whereby the easycleaning and mspecing thereofv and the removal of the .fusible plug maybe effected.

Another object is to provide a closure plug for the cage which is sosecured within the cage that the threads are protected from steam on theone side and fire and resulting carbon deposits on theother. Anotherobject is to provide for the removal of the plug from the cage withoutdamage to the securing threads. I

Other objects will become apparent in the further description of myinvention relat- 7 ing to the accompanying drawings and the It's one. ofthe primary objects of this ina which there will be less likelihood ofthe struction respond quicklyto the heat of the essentialcharacteristics thereof will'be summarized in the claims.

In the drawings wherein I have illus trated the preferred form of myinvention, Fig 1 is a substantially central longitudina cross-sectionthroughthe water alarm; Fig. 2 is a transverse section through thecommunicating passageways in the cage as indicatedby the line 2-2 1nFig. 1.

The invention is primarily concerned with the construction of thefusible plug cage which is shown as inserted from within the fire boxinto the crown sheet and in which am Is angular internal surfacesprovide for ltS IGildY insertion and removal. In the cylindrical chamberadjacent these surfaces the heat conducting and chamber sealing plug isprovided with a flange below the securing threads fitted to form aconvenient seal and which when the plug is being removed, scrapes offthe accumulated cinders from the cylindrical 'walls of the cage. Thelength of the longitudinal openings leading from the fusible .plug tothe alarm conduit has been increased, and the surplus metal surroundingthese passages,

shown in my prior application, above referred to, has been removedsubstantially throughout their entire length. 'The construction of thefusible metal container has been simplified and extends below the "wallirito a large cavity formed in the closure p g- 3 In the drawings ashort section of the crown sheet is shown at 1 and a similar portion ofthe roof sheet at 2. The space between these sheets has beenconsiderably foreshortened for the purpose of more clearly illustratingmy invention and it is to be assumed that a portion of this space isoccupied normally by water, the level of which is of course always belowthe roof sheet. The conduit for the live steam which accumulatesadjacent the roof sheet is pro vided with a stufling box sleeve 10 shownas having an elbow 11 communicating by way of the pipe 12 and acombination union nut and elbow 13 with the downwardly extendingcentralpipe 16.

' The cage 17 which receives the lower end of the pipeat 18 comprises asubstantially cylindrical lower portion 19 externally threaded at 20 forengaging the crown. sheet and having an angularly formed socket 21 forsecuring, the sleeve within the crown sheet for removing it therefrom bya wrench. An adjacent cylindrical portion 22 rising therefrom is ofslightly greater. diameter than that of the roots of the threads 24which are engaged by threads on a closure plug 26.

Slightly above the threaded portion this chamber terminates in a. heavytransverse wall. The cylindrical exterior of the ,cage merges into amore compact section, having openings therethrough as shown in the crosssection, Fig. 2. At the upper end the cage again assumes the cylindricalshape and is shown as threaded at 30 complementary to the bell mouthedlower end of a tube 31.

The top of the-cage is shown as having a cylindrical groove 32 intowhich the passages 28 extend. The central opening 36 in the cage isthreaded to receive the fusible,

plug 37. The fusible metal 39 normally fills a conical opening in thefusible plug 37 which narrows at the bottom and terminates in theaperture 40 in the head of the fusible plug The head which is preferablyhexagonal in shape to facilitate removal, also has a through transverseopening 41 and it is shown as depending within the cup-shaped upper endof the closure plug 26. The rim on the closure plug formed by thiscavity seats against the transverse wall of the cage thereby forming aneffective stop for the plug, which also increases the area of heatconducting contact surfaces.

The fusible metal 39 is coextensive with the threaded portion of theplug 37, that is to say it does not extend either above or below theposition of the plug which contacts with the transverse wall 27, and itis thereby entirely subjected to the most direct conductivity of heatfrom the firebox through the plug 26 and the walls of the cage.

By virtue of the seal formed at this point and the annular flange 46,formed below the threads on the plug, the threads are well protectedagainst corrosion and abrasion when removing plug and may be formed withan adequate amount of root and apex clearance for facilitating theremoval of the plug. This construction affords the most effectiveconductivity between the closure plug and the upper wall of the cage.The size of the neck 47 connecting the upper threaded portion of theclosure plug with the lower angularly formed head 48 is determined byexperiment so that the proper amount of heat may be conducted from theboiler to the fusible metal 39.

The dome sleeve 1O supports the outer conduit tube 31 and is providedwith the usual packing gland 50 and nut 51. At the upper end of thistube, I provide an elbow 52 which has an enlarged central cavity 53 anda conical roof 54. The alarm which is preferably a whistle such as shownat 55 is threaded into this elbow at 56 and carries a member 57 having areceptacle facing the opening in the cavity 53* for trapping the fusedmetal. i

It will be seen that I have provided a low water alarm, the componentparts of which are extremely simple to manufacture, which may be easilytaken apart for inspection and quickly reassembled when desired. Thereplacement of the fusible element is easily accomplished from withinthe firebox. it being only necessary to remove the plug 26 and themember 37 A very important advantage of this invention, it will be seen,is that this replacement may be accomplished while the water remains inthe boiler. Of course, as the. removal of these plugs opens the steampassages, there must be no steam pressure in the boiler, but the amountof water in the boiler is immaterial and does not interfere with thisreplacement. Moreover by reason of the construction set forth,particularly with reference to the 'quatrefoil cross section of the plugcage at the low water danger point and the contiguity of the surroundingmetal from the crown sheet, the device is made extremely sensitive andquick acting when the water in the boiler falls to a dangerously lowlevel.

A specific advantage is that the hexagonal head of the plug carrying thefusible metal allows convenient removal and replacement, while thecupped threaded head of the plug 26 provides for bypassing heat from thefire box around the fusible plug head to the fusible metal, and assuresopen communication of the passages.

Having thus described my invention, I claim:

1. The combination in a low water alarm, of a passage leading from thesteam space to a signal member formed by adjacent tubesextending'through the roof sheet, a cage to which the tubes arethreaded, said cage being threaded into the crown sheet and having adownwardly facing cavity and channels opening into the cavity andcompleting communication between the tubes, a removable plug in one ofsaid channels adapted to normally interrupt said communication andhaving a passageway therethrough and a fusible member normally closingsaid passageway, a closure member a cavity and longitudinal passagesopening ,thereinto, one of which communicates with the tubular memberleading from the steam space, anqther with the member leading to thesignal, a closure for said cavity having a cupped inner end in intimatecontact with the cage and a shank in spaced relation to the cage andextending into the fire box, a

fusible metal plug in one of said passages normally lnterruptlngcommunication between one of-sald members. and the cavity,

said plug having a recessed head projecting to a member threaded into anopening in the crown sheet and extending upwardly therefrom, having adownwardly facing cavity and having a wall through which a plurality ofopenings communicate with the tubes and with said cavity, a plug for oneof the tubes having a passage therethrough closed by a fusible material,said fusible material normally interrupting the passage of steam tothe'signal rand said plug having a head projecting into said cavity bywhich it may be removed and replaed, a closure for the cavity includinga member havinga shank extending downwardly toward the fire space andthreaded into the cavity, and having an upwardly facing recess separatedfrom said head and surrounding it, the upper edges of the said memberseating against said wall whereby to protect the threads on said memberagainst corrosive effects of foreign matter entering the passages.

4. In combinationin a low water alarm, of a passage leading from thesteam space to a signal member formed of tubes extending through theroof sheet, a cage threaded into the crown-sheet into which the tubesare threaded "having a downwardly facing cavity partially threaded andpartially smooth and an opening completing communication between thetubes, a plug in one of saidopenings adapted to normally interrupt saidcommunication and having a fusible portion and means forfl'removing saidplug, a cupped closure member surrounding said means, threaded into saidcavity and extending toward the fire box space and adapted to by-passheat from the fire box through thecage t0 the fusible plug, and a flangebelow the threaded portion of the cavity closely fitting the smoothportion, whereby the threads are protected against scale.

5. In combination, a boiler having a crown sheetand a roof sheet, and apair of tubes extending into the roof sheet, one communicating with thesteam space and the other with a steam operated signal, a member securedto the crown sheet and having a passageway afi'ording communicationbetween the inner ends of said tubes, a 11g comprising fusible materialnormally closing said passageway, said member having a cavity openinginto the fire space and a closure member for the cavity threaded intosaid cavity and arranged to by-pass heat from the fire space to saidplug through the wall of said member, and means comprising an outwardlyextending flange of greater. diameter than the top of the threads on theclosure member, closely fitting the cavity below the threaded portion,whereby the threads are protected against damage by foreign matterdeposited in the cewity.

6. In a low water alarm for a boiler, in combination, a crown sheet anda roof sheet having an opening therein, apair of tubes extending throughsaid opening, a cage secured to the crown sheet and rigid with saidtubes, said cage having a cavity and passageways communicating with bothtubes and said cavity, a plug containing fusible material located withinone of said passageclosing communication between one of the tubes andsaid cavity and extending downwardly into the cavity,'a closure memberthreaded into the cage and having a re-' cess surrounding the downwardlyextending portion of the plug, said closure member seating against theroof of the cavity whereby to protect the threads of the closure memberagainst corrosion, and said closure member having a portion thereofextending into the fire space.

7. A low water alarm for a boiler having a roof sheet and a crown sheet,a pair-oftubes extending through the roof sheet,on'e leading to thesteam space and the other to a slgnal device, a cage member secured tothe crown sheet and rigid with the inner endsof said tubes, said cagehaving passageways communicating with both the tubes, one of saidpassageways having a plug therein closing such communication to one ofthe tubes, said plug having a recess partially filled with fusiblematerial, a passageway extending transversely of said recess, a closuremember threaded into the cage and in intimate contact therewith at itsupper end along its top and side surfaces and having a pocket in itsupper face'into which the lower end of said plug extends, said pocketbeing arranged to receive the fused material when the alarm is actuated,and said lateral passageways serving to direct steam through the plugfrom the tube normally closed thereby and into the passageways in thecage leading to the other tube. v

8. In a low water alarm for a boiler having a roof sheet and crownsheet, a pair of tubes extending through the roof sheet, onecommunicating with the steam space and the other with a signal, a cagemember secured to the crown sheet and rigid with the inner ends of saidtubes, a transverse wall in the cage having openings therethrough, oneof the openings communicating with one of the tubes and onecommunicating with the other tube, said latter opening being normallyclosed by a plug having a passage closed by fusible material, the cagemember having a cavity communicating with the said openings, and aclosure member in intimate contact with the cage adjacent the roof ofsaid cavity, the lower end of said closure memher being separated fromthe cage in the zone of engagement of the cage by the crown sheetwhereby heat from the fire space is by-passed from the closure memberthrough the cage to the fusible plug in a region well above the crownsheet.

9. A low wateralarm for avboiler having a root sheet and a crown sheet,a pair of tubes extending through the roof sheet one within'the other,one of said tubes communicating with the steam space of the boiler andthe other with a steam operated signal, a member secured to the crownsheet of the boiler and having a cavity therein, a central passagewayleading from the inner tube to said cavity and a series of verticalpassageways communicating between the outer tube and the cavity anddisposed about said central passageway, a plug'having fusible materialforming a portion thereof normally cl0sing said central passageway, saidmaterial being located in the Zone of the vertical pas- 'sageway, meansfor conducting heat from the fire space'to the fusible material, thebody of the cage having indentations between the passageways, wherebythe heating efiect of steam in the boiler augments the heat conductedfrom the fire space to fuse said material when the water in the boilerfalls below said passageways. I

In testimony whereof, I hereunto affix my signature.

HERMAN B. THURSTON.

